The present invention relates to a power transmission apparatus disposed on a power transmission path between a driving device and driven device and added with a torque limiter function of disconnecting power transmission when an overload acts.
Various types of power transmission apparatuses are conventionally proposed to be used in a compressor for an automobile air conditioner or the like. As shown in U.S. Pat. No. 6,200,221 and Japanese Patent Laid-Open No. 2003-56595, a power transmission apparatus of this type comprises a damper mechanism. Rotation of a driving rotary body is transmitted to a driven rotary body through the damper mechanism.
In a conventional power transmission apparatus shown in FIG. 16, reference 2 denotes a compressor (driven device) for an automobile air conditioner; 3, a housing for the compressor 2, 4, a pulley (driving rotary body) which is rotatably mounted on a cylindrical portion 3A of the housing 3 through a bearing 5; 6, a rotating shaft of the compressor 2; 7, a hub (driven rotary member) mounted on the rotating shaft 6; 8, a rotation transmission member which connects the pulley 4 to the hub 7; 9, a damper mechanism which connects the pulley 4 to the rotation transmission member 8; and 11, a holding plate 11 which constitutes a driven rotary body 12 together with the hub 7. These constituent elements constitute a power transmission apparatus 1 of the compressor 2.
The rotation transmission member 8 comprises an almost disc plate-like main body 8A, a plurality of fixing portions 8B projecting from the outer periphery of the main body 8A equidistantly in a circumferential direction, arcuate connecting portions 8C extending from the respective fixing portions 8B along the outer periphery of the main body 8A and elastically deformable in the direction of thickness, and connecting portions 8D extending from the distal ends of the respective connecting portions 8C. In the rotation transmission member 8, a set screw 10 fixes the corresponding fixing portion 8B to the pulley 4 through the damper mechanism 9. Elastic deformation of the connecting portion 8C interposes the corresponding connecting portion 8D between holding portions 7C and 11B of the hub 7 and holding plate 11 to releasably hold the connecting portion 8D.
The damper mechanism 9 serves to absorb the shock or torque fluctuations during power transmission and comprises an elastic member (to be referred to as a rubber damper hereinafter) 16 and connecting member 19. The damper mechanism 9 comprises, e.g., three damper mechanisms 9 built into a damper holding member 15 equiangularly in the circumferential direction. The damper holding member 15 is disposed in an annular recess 17 of the pulley 4 and has three storing portions 18 which respectively store the corresponding damper mechanisms 9. The rubber damper 16 forms a cylinder with two open ends and is built into the corresponding storing portion 18 together with the connecting member 19. The connecting member 19 forms a flanged cylinder having female threads, and the rubber damper 16 is fitted on its outer surface. The set screw 10 fixes the fixing portion 8B of the corresponding rotation transmission member 8 to the front end face (hub-side end face) of the connecting member 19, so a flange 19A provided at the rear end of the connecting member 19 urges the rubber damper 16 against the inner surface of a disc plate 4A of the pulley 4.
In this power transmission apparatus, power from the automobile engine (driving device) is transmitted to the rotating shaft 6 through the pulley 4, damper mechanisms 9, rotation transmission member 8, and driven rotary body 12.
In the damper mechanism 9, the rubber damper 16 effectively absorbs the torque fluctuations or shock transmitted from the pulley 4 to the driven rotary body 12 during power transmission. Thus, a tension that acts on the connecting portion 8D of the rotation transmission member 8 due to the torque fluctuations or shock during power transmission is reduced, and the connecting portion 8D will not come out from the portion between the hub 7 and holding plate 11.
When an overload acts on the compressor 2 side, it suppresses rotation of the rotating shaft 6 to generate a rotation force equal to or more than a predetermined magnitude between the pulley 4 and hub 7. This rotation force disconnects the pulley 4 and hub 7 that have been connected by the rotation transmission member 8. More specifically, when rotation of the rotating shaft 6 is suppressed, the rotation force generated between the pulley 4 and hub 7 releases the connecting portions 8D of the rotation transmission member 8 from the portion between the holding portions 7C and 11B of the hub 7 and holding plate 11 to disconnect the pulley 4 and driven rotary body 12 from each other. The connecting portions 8C are then elastically restored to move the connecting portions 8D to the rear side of the holding plate 11. Therefore, once the connecting portions 8D are released, the rotation transmission member 8 and driven rotary body 12 do not interfere with each other, and rotation transmission from the pulley 4 to the rotating shaft 6 can be readily disconnected.
In the conventional power transmission apparatus 1 described above, the holding portions 7C and 11B of the hub 7 and holding plate 11 releasably hold the connecting portions 8D of the rotation transmission member 8. The connecting portions 8C are elastically deformed toward the pulley 4, and the set screws 10 fix the fixing portions 8B to the connecting members 19 of the damper mechanisms 9. Thus, the elastic restoration force of the connecting portions 8C acts on a bearing (not shown) that axially supports the rotating shaft 6 as a rightward thrust load. Consequently, the rotation resistance of the bearing increases to result in the loss of the driving energy of the compressor 2. The elastic restoration force of the connecting portions 8C also acts on the bearing 5 that axially supports the pulley 4 as a thrust load in a direction (leftward in FIG. 16) opposite to that described above.
As a conventional apparatus in which the above problems are solved, a power transmission mechanism disclosed in Japanese Patent Laid-Open No. 2003-56595 is known. In this power transmission mechanism, a hub and rotation transmission member hold the head of a torque transmission pin (connecting member) which constitutes a damper mechanism together with a rubber damper. A pin main body is pressed into the rubber damper to be movable forward/backward. The hub has a groove where the head of the pin escapes when an overload acts.
In this arrangement, when an overload acts on the compressor side, the rotation of the rotating shaft is suppressed to generate a rotation force equal to or larger than a predetermined magnitude between a pulley and the hub. This rotation force releases the connecting portion of the rotation transmission member from a portion between the hub and a holding plate, thereby disengaging the pulley and hub from each other. When the connecting portion is released from the portion between the hub and holding plate, the elastic restoration force of the connecting portion extracts the pin main body of the torque transmission pin from the rubber damper, and the head of the pin moves to the groove in the hub. Thus, the pulley idles to disconnect power transmission from the engine to the compressor. As a result, the load on the engine on the compressor side can be eliminated.
In this structure, the pin main body of the torque transmission pin is pressed into the rubber damper to be movable forward/backward. Thus, the elastic restoration force of the connecting portion of the rotation transmission member does not act as a thrust load on bearings that support the rotation shaft and pulley, thereby solving the above problems.
In the conventional power transmission apparatus, however, when an overload acts, the pin main body of the torque transmission pin is extracted from the rubber damper and the head of the pin is moved to the groove of the hub. To connect the torque transmission pin and rubber damper firmly, the pin main body of the torque transmission pin must be long, the head of the pin must be thick, and the groove must be deep. This increases the size of the apparatus in the axial direction. As a result, the apparatus cannot be made compact.
If the pin main body is long, to support the thick head of the torque transmission pin with the fixing portion of the rotation transmission member, the span of the connecting portion must be long to increase the elastic deformation amount. This increases the size of the rotation transmission member.